3-Alkoxyisoxazol-4-yl-substituted 2-amino carboxylic acid compounds

ABSTRACT

(3-Alkoxyisoxazol-4-yl)-substituted 2-amino carboxylic acid derivatives and sulfur analogues thereof having general formula (I) or (II),                    
     wherein R 1  is hydrogen, alkyl, alkenyl, alkynyl, cycloalk(en)yl, cycloalk(en)yl-alk(en/yn)yl or optionally substituted phenyl-alk(en/yn)yl; A is a bond or a hydrocarbon spacer group; B is a group —CR a (NR b R c )—COOR 5  wherein R a -R c  are independently hydrogen or alkyl, and R 5  is defined as R 1  or pivaloyloxymethyl, or B is a group of Formula (III),                    
     wherein R 2 , R 3  and R 4  are independently selected from hydrogen, a non-aromatic hydrocarbon group, phenyl- and thienyl-alkyl, and a hetero aliphatic group, or R 3  and R 4  are connected, thereby forming an alkylene, alkenylene or alkynylene group, or R 4  and R 2  are connected in order to form an alkylene, alkenylene or alkynylene group, optionally substituted with hydroxy or methyl, or to form CH 2 —O—CH 2 ; E is COOR 6 , where R 6  is defined as R 5 , or E is a tetrazolyl or triazolyl; X is O or S; and Y is O or S; are excitatory amino acid (EAA), in particular AMPA and/or NMDA receptor ligands, useful in the treatment of cerebral ischaemia, Huntington&#39;s disease, epileptic disorders, Parkinson&#39;s disease, Alzheimer&#39;s disease, schizophrenia, pain, depression and anxiety.

This application is a 371 of PCT/DK97/00426 filed Oct. 3, 1997.

FIELD OF THE INVENTION

The present invention relates to a novel class of(3-alkoxyisoxazol-4-yl)-substituted 2-amino carboxylic acid derivativesand sulfur analogues thereof. The compounds are excitatory amino acid(EAA) receptor ligands, in particular AMPA and/or NMDA receptor ligandsuseful in the treatment of cerebral ischaemia, Huntington's disease,epileptic disorders, Parkinson's disease, Alzheimer's disease,schizophrenia, pain, depression and anxiety.

BACKGROUND OF THE INVENTION

As a result of extensive studies of excitatory mechanisms in the centralnervous system (CNS) during the past three decades, there is now aconsensus of opinion that (S)-glutamate (Glu) is the major EAAneurotransmitter in the CNS (Lodge, D. Excitatory Amino Acids in Healthand Disease. J. Wiley & Sons: Chichester, 1988; Wheal, H.; Thomson, A.Excitatory Amino Acids and Synaptic Transmission. Academic Press:London, 1991; Meldrum, B. S. Excitatory Amino Acid Antagonists.Blackwell Sci. Publ.: Oxford, 1991; Krogsgaard-Larsen, P.; Hansen, J. J.Excitatory Amino Acid Receptors: Design of Agonist and Antagonists. E.Horwood: Chichester, 1992). Glu-operated neurotransmission is mediatedby a large number of receptors, classified into at least fourheterogeneous families of receptors named NMDA, AMPA, kainic acid, andmetabotropic classes of receptors (Monaghan, D. T., et al. Ann. Rev.Pharmacol. Toxicol. 1989,29, 365-402; Watkins, J. C.; Krogsgaard-Larsen,P.; Honoré, T. Trends Pharmacol. Sci. 1990,11, 25-33; Simon, R. P.Excitatory Amino Acids. Thieme Med. Publ.: New York, 1992).

There is very strong evidence supporting the view that excessiveexcitation mediated by EAA receptors (“excitotoxicity”) is a factor ofmajor importance in cerebral ischaemia following stroke, head injury,asphyxia, subarachnoid haemorrhage, cardiac arrest and other situations(Lodge, D., 1988 supra; Meldrum, B. S., 1991 supra). It has been shownin animal models that the damages caused by various ischaemic conditionscan be inhibited by the administration of Glu-antagonists. So, althoughthe relative importance of the different classes of EAA receptors in thephenomena underlying ischaemic insults is unclear, it is generallyagreed that EAA receptor antagonists are potential therapeutic agents inthese conditions.

Accumulating evidence derived from different lines of neurochemical andpharmacological research suggests that derailed EAA receptor mechanisms,possibly including “excitotoxicity”, play a role in Huntington's disease(Young, A. B.; et al. Science 1988,241, 981-983), epileptic disorders(Krogsgaard-Larsen, P.; Hansen, J. J., 1992 supra), Parkinson's disease(Klockgether, T.; Turski, L. Trends. Neurosci. 1989,12, 285-286), andAlzheimer's disease (Greenamyre, J. T.; Maragos, W. F. Cerebrovasc.Brain. Metab. Rev. 1993,5, 61-94; Francis, P. T., et al. J. Neurochem.1993,60, 1589-1604).

Furthermore, central EAA receptors may be involved in the synapticmechanisms underlying schizophrenia (Reynolds, G. P. Trends. Pharmacol.Sci. 1992,13, 116-121), pain and anxiety (Drejer, J. In: ExcitatoryAmino Acid Receptors: Design of Agonists and Antagonists (Eds.Krogsgaard-Larsen, P.; Hansen, J. J.) E. Horwood: Chichester 1992, pp.352-375) and depression (Trullas, R., Skolnick, P., Eur. J. Pharmacol.1990, 185, 1-10 and Trullas et al., Eur. J. Pharmacol. 1991, 203,379-385. So, reduced function of EAA receptors (EAA hypoactivity) seemsto play a role in, for example, schizophrenia (Deutsch, S. I.; et al.Clin. Neuropharmacol. 1989,12, 1-13) and some of the clinical symptomsseen in Alzheimer's disease (Greenamyre, J. T.; et al. Prog.Neuro-Psychopharmacol. & Biol. Psychiat. 1988,12, 421-430). It ispossible that “excitoxicity” as well as EAA hypoactivity are involved inthe complex mechanisms associated with Alzheimer's disease (Greenamyre,J. T.; 1988 supra; Greenamyre, J. T.; Maragos, W. F., 1993, supra).

Accordingly, EEA receptor ligands are considered to be useful in thetreatment of cerebral ischaemia, Huntington's disease, epilepticdisorders, Parkinson's disease, Alzheimer's disease, anxiety,schizophrenia, depression and pain.

Most EAA receptor agonists so far tested, show more or less pronouncedneurotoxicity in model systems and consequently clinical uses of suchcompounds may be limited (Carlsson, M.; Carlsson, A. Trends. Neurosci.1990,13, 272-276) (Willetts, J.; Balster, R. L.; Leander, J. D. Trends.Pharmacol. Sci. 1990,11,423-428).

Partial EAA agonists showing appropriate balance between agonism andantagonism may, on the other hand, have considerable therapeuticinterest, cf. the above indications, (Greenamyre, J. T.; 1988 supra;Christensen, I. T.; et al. Drug. Des. Del. 1989,5, 57-71; Francis, P.T.; et al. J. Neurochem. 1993,60, 1589-1604). Partial agonists may, byvirtue of their EAA antagonist profile, show therapeutically usefulneuroprotection and, at the same time, be sufficiently agonistic toprevent total blockade of the neurotransmission mediated by theparticular EAA receptor.

ATPA, the 5-tert-butyl analogue of AMPA((RS)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid), hasbeen disclosed to be systemically active whereas it has not beenreported to show neurotoxic effects in animals (Ornstein, P. L.; et al.J. Med. Chem. 1993,36, 2046-2048; Lauridsen, J.; Honoré, T.;Krogsgaard-Larsen, P. J.Med.Chem. 1985, 28, 668-672).

Like AMPA itself, a number of mono- and bicyclic AMPA analogues havebeen found to show selective agonist effects at AMPA receptors (Hansen,J. J.; Krogsgaard-Larsen,P. Med. Res. Rev. 1990,10, 55-94;Krogsgaard-Larsen, P.; Hansen, J. J., 1992 supra;). One of theseanalogues, (RS)-2-Amino-3-(3-hydroxy-5-phenylisoxazol-4-yl)propionicacid (APPA), in which the methyl group of AMPA has been replaced by aphenyl group, shows a weak but unique partial agonist profile(Christensen, I. T.; et al., 1989, supra).

ACPA ((RS)-2-amino-3-(3-carboxyoxy-5-methylisoxazol-4-yl)propionic acid)has been described as a potent AMPA receptor agonist (Madsen, U. andWong, E. J. Med. Chem. 1992,35, 107-111).

Furthermore, WO-A1 95012587 discloses a class of (5-arylisoxazol-4-yl)-or (5-arylisothiazol-4-yl)-substituted 2-amino carboxylic acid compoundsas EAA-receptor ligands.

As seen from the above non-neurotoxic, CNS-active EEA receptor ligandswith good penetration into the CNS are highly desirable for treating thevarious diseases mentioned and, accordingly, it is the object of thepresent invention to provide such new drugs.

SUMMARY OF THE INVENTION

It has now been found that a novel class of(3-alkoxyisoxazol-4-yl)-substituted 2-amino carboxylic acid derivativesand sulfur analogues thereof are EAA receptor ligands, in particularAMPA and/or NMDA receptor ligands.

Accordingly, the present invention relates to a novel class of compoundshaving general Formula I or II

wherein R₁ is hydrogen, C₁₋₆ alkyl, C₂₋₆ alkenyl, C₂₋₆ alkynyl,cycloalk(en)yl, cycloalk(en)yl-C₁₋₆ alk(en/yn)yl or phenyl-C₁₋₆alk(en/yn)yl the phenyl group being optionally substituted with CF₃,halogen, C₁₋₆ alkyl or C₁₋₆ alkoxy;

A is a bond or a spacer group selected from C₁₋₆ alkylene, C₂₋₆alkenylene or C₂₋₆ alkynylene, and cycloalkylene;

B is a group —CR_(a)(NR_(b)R_(c))—COOR₅ wherein R_(a)-R_(c) areindependently hydrogen or C₁₋₆ alkyl, and R₅ is defined as R₁ orpivaloyloxymethyl, or B is a group of Formula III

 wherein R₂, R₃ and R₄ are independently selected from the groupconsisting of

a) hydrogen, C₁₋₆ alkyl, C₂₋₆ alkenyl, C₂₋₆ alkynyl, cycloalk(en)yl,cycloalk(en)yl-C₁₋₆ alk(en/yn)yl, phenyl-C₁₋₆ alkyl, thienyl-C₁₋₆-alkyl,and

b) C₁₋₆ alkyl, C₂₋₆ alkenyl and C₂₋₆ alkynyl in which one or more carbonatoms are replaced by N, O, and/or S; or

R₃ and R₄ are connected thereby forming a C₂-C₆ alkylene, C₂-C₆alkenylene or C₂-C₆ alkynylene group; or

R₄ and R₂ are connected in order to form a C₁-C₃ alkylene, C₂-C₃alkenylene or C₂-C₃ alkynylene group optionally mono- or di-substitutedwith hydroxy or methyl, or to form CH₂—O—CH₂;

E is COOR₆, where R₆ is defined as R₅, or E is tetrazol-5-yl,1,2,4-triazol-3-yl or 1,2,3-triazol-4-yl

X is O or S; Y is O or S; and

pharmaceutically acceptable salts thereof.

In another aspect, the invention relates to a method for the preparationof the novel compounds of Formula I or II.

In yet another aspect, the invention relates to a pharmaceuticalcomposition comprising a novel compound of Formula I or II together witha suitable pharmaceutically acceptable carrier or diluent.

In yet another aspect, the invention relates to the use of a compound ofFormula I or II for preparing a pharmaceutical composition for treatmentof cerebral ischaemia, Huntington's disease, epileptic disorders,Parkinson's disease, Alzheimer's disease, schizophrenia, pain,depression or anxiety.

Some compounds of the invention have been found to be AMPA receptorligands with affinities in micromolar concentrations and some compoundshave been found to bind to NMDA receptors. Furthermore, some of thecompounds of the invention were found to be agonists whereas others werefound to be antagonists. Thus the compounds of the invention are usefulin the treatment of cerebral ischaemia, Huntington's disease, epilepticdisorders, Parkinson's disease, Alzheimer's disease, schizophrenia,pain, depression and anxiety. The compounds wherein R₅ and/or R₆ are nothydrogen are prodrugs for the corresponding compounds wherein R₅ and R₆are hydrogen.

DETAILED DESCRIPTION OF THE INVENTION

Some of the compounds of general Formula I or II may exist as opticalisomers thereof, and such optical isomers are also embraced by theinvention.

In general Formula I and II, the term C₁₋₆ alkyl is intended to mean astraight chain or branched alkyl group having from 1 to 6 C atoms,inclusive, such as methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl,2-methyl-2-propyl etc. Similarly, C₂₋₆ alkenyl and C₂₋₆ alkynyldesignate such straight chain or branched groups having 2 to 6 C-atomsand C₁₋₆ alkylene, C₂₋₆ alkenylene and C₂₋₆ alkynylene designate suchbranched or straight chain divalent groups. Cycloalkyl designates such agroup having 3-7 carbon atoms and the term C₁₋₆-alkoxy designates suchgroups having a C₁₋₆ alkyl, C₂₋₆ alkenyl or C₂₋₆ alkynyl moiety asdefined above.

The term “alk(en/yn)yl” means that the group may be an alkyl, alkenyl oralkynyl group.

The term bond (defined for A) means that B may be attached directly tothe 4-position of the isoxazole ring.

Halogen means fluoro, chloro, bromo or iodo.

Some of the compounds of the general Formula I or II may exist aspharmaceutically acceptable salts thereof which are also embraced by theinvention.

The salts of the compounds of the general Formula I or II are saltsformed with non-toxic organic acids, e.g. maleic, fumaric, benzoic,ascorbic, oxalic, tartaric, lactic and malic acid, or inorganic acids,e.g. hydrochloric, hydrobromic, sulfuric, phosphoric and nitric acid orthey may be salts of inorganic bases such as alkali metal salts, e.g.sodium, potassium, or lithium salts, alkaline earth metal salts, e.g.calcium or magnesium salts, or ammonium salts or salts of organic bases.

In Formula I and II, A is preferably a bond or C₁C₃ alkylene, mostpreferably methylene.

B is preferably —CR_(a)(NR_(b)R_(c))—COOR₅ wherein R_(b)-R_(c) arehydrogen and R_(a) is hydrogen or C₁₋₆ alkyl, conveniently methyl, or agroup of Formula III wherein R₂, R₃ and R₄ are hydrogen or C₁₋₆ alkyl,or R₄ and R₂ are connected in order to form a C₁-C₃ alkylene group. Mostpreferably, B is —CH(NH₂)—COOH or a group of Formula III wherein each ofR₂, R₃ and R₄ are hydrogen.

Preferably, E is COOH, triazolyl or tetrazolyl, preferably COOH. Anothersubgroup comprises the compounds wherein E is COOR₆ where R₆ is not H.According to a preferred subgroup of the compounds of the invention Xand Y are O. Other subgroups are those wherein X is O and Y is S; Y is Oand X is S; and X and Y are S, respectively.

R₁ is preferably C₁₋₆ alkyl, C₂₋₆ alkenyl or C₂₋₆ alkynyl. Particularlysuitable R₁ groups are methyl, ethyl, propyl, butyl and propargyl.

In a preferred embodiment of the invention the compound is a compound ofFormula I wherein A is a bond or C₁-C₃ alkylene, B is —CH(NH₂)—COOH or agroup of Formula III wherein each of R₃, R₄ and R₂ are hydrogen, X and Yare both oxygen, and R₁ is C₁₋₆ alkyl, C₂₋₆ alkenyl or C₂₋₆ alkynyl.Particularly suitable R₁ groups are methyl, ethyl, propyl, butyl andpropargyl.

According to the invention, the compounds of Formula I or II areprepared by the following methods. For the sake of simplicity thereactions a)-e) and g)-h) are only shown for Formula I. Same methods maybe used with respect to Formula II.

a) in order to obtain a compound of Formula I wherein B is a—CR_(a)(NR_(b)R_(c))—COOR₅ wherein R_(a)-R_(c) and R₅ are as previouslydefined, and at least one of R_(b), R₅ and R₆ is hydrogen, deprotectionof a compound of the general Formula IV

 wherein R₁, A, X and Y are as previously defined, R_(a)′-R_(c)′, E′ andR₅′ are defined for R_(a)-R_(c), and E and R₅, respectively, or they areprotection groups, provided that at least one of E′, R₅′ and R_(c)′ is aprotection group;

b) in order to obtain a compound of Formula I wherein B is a—CR_(a)(NR_(b)R_(c))—COOR₅ group wherein R_(b), R_(c) and R₅ are allhydrogen, deprotection of a compound of the general Formula V

 wherein R₁, A, Y, X and E′ are as previously defined;

c) in order to obtain a compound of Formula I wherein B is a group ofFormula III, addition-elimination reaction of a compound of the generalFormula VI with a compound of the general Formula VII:

 in which formulas R₁-R₄, A, X, Y and E′ are previously defined;

d) In order to obtain a compound of Formula I, wherein B is a group ofFormula III wherein R⁴ and R² are linked to form a C₁₋₃ alkylene, C₂-C₃alkenylene or C₂-C₃ alkynylene group optionally mono- or di-substitutedwith hydroxy or methyl, reacting a compound of Formula VIII

 wherein R₁, R₃, A, X, Y and E′ are as previously defined; R₄ and R₂ arelinked to form a group as defined above and BOC is t-butoxycarbonyl,with 3,4-diethoxy-3-cyclobuten-1,2-dion and subsequent ringclosure anddeprotection;

e) in order to obtain a compound of Formula I wherein B is a group ofFormula III and one or more of R₂-R₄ are different from hydrogen,alkylation of a compound of the general Formula IX

 wherein R₁, R₂, R₃, R₄, A, X, Y and E′ are as previously defined, atleast one of R₂-R₄, however, being hydrogen;

f) in order to obtain a compound of Formula I or II, alkylating acompound having general Formula X

 wherein A, X, Y and E′ are as previously defined and B′ is as B exceptthat in the definition of R_(b), R_(c) and R₅ hydrogen is replaced by aprotection group, with an alkylating agent R₁′Z wherein R₁′ is as R₁except that it may not be hydrogen, thereby obtaining a mixture of thecompounds XI and XII:

 wherein A, X, Y, E′ and B′ are as defined above, and then separatingand deprotecting the compounds;

g) in order to obtain a compound of Formula I wherein R₅ and/or R₆ isdifferent from hydrogen, etsterification of a compound of formula XIIIor XIV:

 wherein R₁, R₂, R₃, R₄, A, X, Y and R_(a)-R_(c) are as previouslydefined;

h) in order to obtain a compound of Formula I wherein B is a—CR_(a)(NR_(b)R_(c))—COOR₅ group wherein R_(a), R_(b), R_(c) and R₅ areall hydrogen, and E is COOH in particular an enantiomeric pure compound,subjecting a compound of Formula XV

 to a Schöllkopf Bis-Lactim Amino Acid synthesis and subsequentdeprotection of the obtained bislactim ether having Formula XVI

 in which formulas X, Y, R_(a) and R₁ are as previously defined and A′is as defined for A except that it may not be a bond.

In the method of the invention preferred protection groups are asfollows:

For E=COOH: 4,5-dihydro-4,4-dimethyloxazol-2-yl, C₁₋₆ alkyl or a benzylgroup; for R₅=hydrogen: C₁₋₆ alkyl and R_(b)=hydrogen: C₁₋₆alkylcarbonyl.

The one step deprotection according to method a) is carried out bytreatment of the compound of Formula IV with a suitable aqueous acid,conveniently an 0.5-12 N aqueous solution of HCl, an aqueous solution of48% HBr, or a saturated solution of HBr in acetic acid. The deprotectionmay also be carried out in successive steps by using aqueous acids andaqueous bases, conveniently successively in an aqueous acid such as0.5-12 N HCl, an aqueous base such as 1-8 N NaOH and an aqueous acidsuch as 0.5-12 N HCl, or successively in an aqueous base such as 1-8 NNaOH and an aqueous acid such as 0.5-12 N HCl.

Starting materials of Formula IV are conveniently prepared from3-alkoxy-4-methylisoxazole-5-carboxylic acid (WO95/12587, A1) bycomplete deprotection in an aqueous acid according to the abovedescribed deprotection conditions, optional esterification of the3-hydroxy-4-methylisoxazole-5-carboxylic acid and subsequent alkylationwith an appropriate halide or simply by alkylation. This is followed bybromination of the 4-methylisoxazole group and subsequent alkylationwith an amino acid precursor e.g. diethyl acetamidomalonate. Other4-alkylisoxazoles may be prepared by chain-elongation, e.g. alkylationwith cyanide or diethyl malonate and subsequent transformation to theprimary alkyl halide or aldehyde. The halide may be treated as outlinedabove. The aldehyde may be used as starting material fot the preparationof compounds of general formular V.

In b), the one step deprotection is carried out by treatment of acompound of Formula V with a suitable aqueous acid or aqueous base,conveniently in 0.5-8 N aqueous hydrochloric acid. The deprotection mayalso be performed in successive steps by using aqueous acids and aqueousbases as mentioned above for method a). The hydantoin ring may also becleaved by the use of an aqueous solution of Ba(OH)₂, aqueous 10-70%sulphuric acid or by the use of enzymes such as hydantoinases. Thecleavage of the hydantoin ring may be carried out either before or afterthe deprotection of the E-group. The R₁ group may have to bereintroduced by alkylation after complete deprotection of the hydantoinintermediate.

The hydantoin rings in the compounds of the general Formula V areconveniently formed according to the methods described by Ware,E.,Chem.Rev. 1950, 46, 403-470. The cleavage of the hydantoin ring isconveniently performed in analogy with the methods described by Curry,K. et al J.Med.Chem. 1988, 31, 864-867, Farrington, G. K. et al,J.Med.Chem. 1987, 30, 2062-2067, Grunewald, G. L. et al, J.Med.Chem.1980, 23, 754-758, Hiroi, K. et al, Chem.Pharm.Bull. 1968, 16, 444-447or Stark, G. R. et al, J.Biol.Chem. 1963, 238, 214-226.

The starting material for preparation of compounds of Formula V may beobtained as outlined above for starting materials for method a). If A isa bond, the aldehyde may be prepared from the bromomethyl compound bybromination and subsequent transformation into the aldehyde.

The addition-elimination reaction according to method c) is convenientlyperformed in a protic organic solvent such as an alcohol, preferably inthe presence of a suitable inorganic base such as aqueous NaOH at roomtemperature. The intermediates of Formula VII may be prepared by themethods described by Cohen, S. et al, J.Amer.Chem.Soc. 1966, 88,1533-1536, EP-A2-0496561 or Kinney, W. A. et al, J.Med.Chem. 1992, 35,4720-4726.

The intermediate of the general formula VI is readily obtained by aGabriel synthesis of primary amines as described by Sheehan, J. C. etal., J. Am. Chem. Soc., 1950, 72, 2786-88. The alkyl halide startingmaterials for this synthesis are conveniently obtained as described withrespect to starting materials used in method a), cf. above.

The deprotection is conveniently performed by the use of an aqueous acidor an aqueous base, preferably 0.5-8 N HCl or aqueous 0.5-8 N NaOH,either at room temperature or at elevated temperatures.

In method d), the reaction and the subsequent ringclosure anddeprotection are performed as described by Kinney et al., EP-A2-0496561.

The starting materials of formula VIII may be obtained by reacting e.g.4-bromomethyl isoxazole obtained as described with respect to thestarting materials in method a) with a mono-BOC-proteted alkylenediamine cf. EP-A2-0496561.

The alkylation of compounds of the general Formula IX according tomethod e) is conveniently performed in an inert organic solvent such asa suitable alcohol, ketone or dimethylformamide preferably in thepresence of a suitable base such as sodium hydride, potassium carbonateor triethylamine, as described by Kinney, W. A., EP-A2-0496561. Thestarting materials of formula IX may be obtained by method c).

In method f), deprotection of compounds of general Formulas XI and XIIis accomplished as described in method a) or by using a solution ofhydrochloric acid in diethyl ether or another non-aqueous deprotectionmethod. Starting material X is obtained as described with respect to thestarting materials in method a) above.

In method g), the esterfication may be performed by methods well knownin the art, e.g. treatment with an acidic solution of an alcohol.Starting materials are prepared in accordance with method a)-e) or h).

Resolution of the compounds of general formula I is convenientlyperformed by diastereomeric saltformation using optical active acids orbases, e.g. 1-phenylethylamine. In some cases, the resolution isconveniently performed by formation of diastereomeric compounds andsubsequently separation of the diastereomers by flash chromatography orcrystallisation. Certain diastereomers may conveniently be prepared byasymmetric synthesis by using Schöllkopf's Bis-Lactim Amino Acidsynthesis, cf. method h). In this synthesis, starting materials arealkyl halides obtained as described above for starting materials formethod a). The protecting group for the 5-carboxyisoxazole group ispreferably an 2-oxazoline group prepared from the corresponding5-cyanoisoxazole (WO95/12587, A1) by condensation with an aminoalcohol.

Salts of the compounds of the invention are easily prepared by methodswell known in the art, i.e. by reacting the compound with either theequivalent amount of acid or base in an aqueous miscible solvent, suchas acetone or ethanol, with isolation of the salt by concentration andcooling, or reacted with an excess of the acid or base in an aqueousimmiscible solvent such as ethyl ether or chloroform, with the desiredsalt separating directly. These salts may also be prepared by theclassical method of double decomposition of appropriate salts.

The compounds of general Formula I and the pharmaceutically acceptableacid addition salts thereof may be administered in any suitable way,e.g. orally or parenterally, and the compounds may be presented in anysuitable form for such administration, e.g. in the form of tablets,capsules, powders, syrups or solutions or dispersions for injection.

An effective daily dose of a compound of general Formula I or apharmaceutically acceptable salt thereof is from 10 μg/kg to 50 mg/kgbody weight.

EXAMPLES

In the following the invention is further illustrated by way of exampleswhich may in no way be construed as limiting for the invention.

All melting points were determined on a Büchi SMP-20 apparatus and areuncorrected. ¹H NMR and ¹³C NMR spectra were recorded on a Brucker 250MHz spectrometer (250.13 MHz for ¹H NMR and 62.90 MHz for ¹³C NMR) usingTMS as an internal standard if not otherwise stated.

Mass spectra were obtained on a Quattro MS-MS system from VG Biotech,Fisons Instruments connected to an HP 1050 modular HPLC system. 20-50 μlof sample (10 μg/ml) dissolved in a mixture of 1% acetic acid inacetonitrile/water=1:1 or in a mixture of acetonitril/water/aqueousammonia (25%)=25:25:1 (zwitterions) was introduced via the autosamplerat a flow of 30 μl/min into the Electrospray Source. Spectra wererecorded at standard conditions to obtain molecular weight information((M+H)⁺) or ((M−H)). The background was subtracted.

Analytical HPLC was carried out on a 150×4.6 mm Lichrocart 250-4 (Merck)column eluted at 35° C. with 1 mL/min of methanol/0.01 M ammoniumacetate, pH 8=3:2. The instrumentation used consisted of a L6200 HPLCpump, a L5025 column thermostat and a L4000A UV-VIS detector (set at 230nm). Diastereomeric purities expressed as diastereomeric excess (de)were calculated from peak areas.

Chiral HPLC analysis was performed on a 150×4.6 mm Sumichiral OA-5000column eluted at ambient temperature with 1 mL/min of 5 mM CuSO₄ (aq).The instrumentation used consisted of an AS 2000 autosampler, a L6200HPLC pump, a T6300 column thermostat, a L4250 UV-VIS detector (set at240 nm), and a D 6000 computer interface, all from Merck-Hitachi.Enantiomeric purities expressed as enantiomeric excess (ee) werecalculated from peak areas.

Example 1 (RS)-2-Amino-3-(5-carboxy-3-methoxyisoxazol-4-yl)propionicAcid Hydrate (Comp. 1) 1) 3-Hydroxy-4-methylisoxazole-5-carboxylic Acid

3-Ethoxy-4-methylisoxazole-5-carboxylic acid (15 g, 88 mmol) and 47% HBr(aq) (150 mL) was boiled under reflux for 6 h. The solution was cooledand crystalline title compound was collected by filtration (8.7 g, 69%):mp 257-259° C. The acidic filtrate was added water (100 mL), andextracted with diethyl ether (6×400 mL). The organic extracts werewashed with brine (100 mL), dried (MgSO₄) and concentrated in vacuo togive crude title compound (3.0 g, 24%). Overall yield of 93%. A mixtureof the two crops were used in the next step.

2) Ethyl 3-Hydroxy-4-methylisoxazole-5-carboxylate

3-Hydroxy-4-methylisoxazole-5-carboxylic acid (6.0 g, 42 mmol) and asaturated solution of HCl in EtOH (110 mL) was boiled under reflux for 4h. The solution was concentrated in vacuo and the residue dissolved inEtOAc, dried (MgSO₄) and evaporated in vacuo to give crude titlecompound (7.2 g, 100%). A small sample was recrystallized(EtOAc/heptane) to give colorless crystals: mp 133-134° C. The crudeproduct was used in the next step without further purification.

3) Ethyl 3-Methoxy-4-methylisoxazole-5-carboxylate

A mixture of ethyl 3-hydroxy-4-methylisoxazole-5-carboxylate (1.0 g, 5.8mmol), methyl iodide (0.4 mL, 5.8 mmol) and K₂CO₃ (1.6 g, 11.7 mmol) inDMF (40 mL) was heated at 40° C. for 1 h. The mixture was poured onto anice/water mixture (100 mL) and extracted with diethyl ether (3×100 mL).The organic extracts were washed with water (2×50 mL), brine (50 mL),dried (MgSO₄) and concentrated in vacuo (0.8 g, 74%). The procedure wasrepeated in order to obtain crude product equivalent to 17.5 mmol ofstarting material which was subjected to flash chromatography (silicagel, eluent: dichloromethane/diethyl ether=9:1) affording crude titlecompound as a yellow oil (1.4 g, 43%) which was used in the next stepwithout further purification.

4) Ethyl 4-(Bromomethyl)-3-methoxyisoxazole-5-carboxylate

Ethyl 3-Methoxy-4-methylisoxazole-5-carboxylate (1.3 g, 7.0 mmol), NBS(1.4 g, 7.9 mmol), dibenzoyl peroxide (catalytic amount) andtetrachloromethane (40 mL) was boiled under reflux for 10 h. The mixturewas cooled, filtered and concentrated in vacuo to give crude titlecompound as a yellow oil (1.8 g, 97%). The crude product was used in thenext step without further purification.

Ethyl2-Acetamido-2-(ethoxycarbonyl)-3-[5-(ethoxycarbonyl)-3-methoxyisoxazol-4-yl]proionate

A mixture of diethyl acetamidomalonate (1.6 g, 7.4 mmol) and potassiumtert-butoxide (0.9 g, 8.0 mmol) in N-methylpyrrolidone (30 mL) wasstirred at room temperature for 30 min. Ethyl4-(bromomethyl)-3-methoxyisoxazole-5-carboxylate (1.8 g, 6.8 mmol) inN-methylpyrrolidone (10 mL) was added (temp 22-28° C.) and the resultingmixture was stirred at room temperature for 1.5 h. The reaction mixturewas poured onto an ice/water mixture (100 mL) and the aqueous phase wasextracted with EtOAc (3×150 mL). The organic extracts were washed withan aqueous solution of potassium tert-butoxide, water (100 mL) and brine(100 mL), dried (MgSO₄) and concentrated in vacuo. Flash chromatography(silica gel, eluent: EtOAc/heptane=1:1) afforded crude title compound(1.8 g, 66%). A small sample was recrystallized (EtOAc/heptane) to givecolourless crystals: mp 78-80° C. The crude product was used in the nextstep without further purification.

6) (RS)-2-Amino-3-(5-carboxy-3-methoxyisoxazol-4-yl)propionic AcidHydrate (Comp. 1)

A suspension of ethyl2-acetamido-2-(ethoxycarbonyl)-3-[5-(ethoxycarbonyl)-3-methoxyisoxazol-4-yl]propionate(1.2 g, 3.0 mmol) in 0.5 M HCl (100 mL) was boiled under reflux for 48h. The mixture was cooled, washed with dichloromethane (100 mL) anddiethyl ether (2×100 mL), filtered and concentrated in vacuo. Water wasadded (5 mL) and the pH adjusted to about 3 by addition of NaOH (0.1 Mand 1 M). The aqueous phase was reduced in vacuo (2 mL) and aprecipitate collected by filtration. The precipitate was stirred inwater (2 mL) at room temperature for 24 h affording Comp. 1 afterfiltration (70 mg, 10%): mp 222-225° C. (dec); ¹H NMR (DMSO-d₆) δ2.88(dd, 1 H), 3.01 (dd, 1 H), 3.85-3.96 (m, 1 H), 3.90 (s, 3 H); ¹³C NMR(DMSO-d₆) d 22.70, 52.38, 57.32, 103.25, 159.43, 165.95, 170.66 (2 C);MS ((M+H)⁺) m/z 231. Anal. (C₈H₁₀N₂O₆.0.25H₂O) calcd, C, 40.94; H, 4.51;N, 11.94; found, C, 41.01; H, 4.37; N, 11.91.

The following compounds were prepared in a similar way:

(RS)-2-Amino-3-(5-carboxy-3-ethoxyisoxazol-4-yl)propionic Acid (Comp.2).

Mp 238-240° C. (dec); ¹H NMR (DMSO-d₆) d 1.34 (t, 3 H), 2.90 (dd, 1 H),3.03 (dd, 1 H), 3.96 (dd, 1 H), 4.23 (q, 2 H); ¹³C NMR (DMSO-d₆) δ14.46,22.41, 51.89, 65.63, 103.34, 159.22, 164.97, 169.75, 170.40; MS ((M+H)⁺)m/z 245. Anal. (C₉H₁₂N₂O₆) calcd, C, 44.27; H, 4.95; N, 11.47; found, C,44.10; H, 4.92; N, 11.34.

(RS)-2-Amino-3-(5-carboxy-3-isopropoxyisoxazol-4-yl)propionic Acid(Comp. 3)

Mp 242-243° C. (dec); ¹H NMR (DMSO-d₆) d 1.32 (dd, 6 H), 2.88 (dd, 1 H),3.01 (dd, 1 H), 3.96 (dd, 1 H), 4.79 (h, 1 H); ¹³C NMR (DMSO-d₆) δ21.57,21.77, 22.35, 51.82, 73.13, 103.56, 159.22, 164.91, 169.08, 170.36; MS((M+H)⁺) m/z 259. Anal. (C₁₀H₁₄N₂O₆) calcd, C, 46.51; H, 5.46; N, 10.85;found, C, 46.37; H, 5.46; N, 10.83.

(RS)-2-Amino-3-(5-carboxy-3-hydroxyisoxazol-4-yl)propionic Acid Hydrate(Comp. 4)

Mp 175-177° C.; ¹H NMR (DMSO-d₆) δ3.00 (d, 2 H), 3.88 (t, 1 H); ¹³C NMR(DMSO-d₆) δ23.07, 52.07, 105.84, 159.41, 162.11, 169.89, 170.78; MS((M+H)⁺) m/z 217. Anal. (C₇H₈N₂O₆.0.25H₂O) calcd, C, 38.10; H, 3.88; N,12.70; found, C, 37.72; H, 3.98; N, 12.52.

Example 2(RS)-2-Amino-3-(5-carboxy-2,3-dihydro-2-methyl-3-oxoisoxazol-4-yl)propionicAcid Hydrate (Comp 5) Ethyl2,3-Dihydro-2,4-dimethyl-3-oxoisoxazole-5-carboxylate

A mixture of ethyl 3-hydroxy-4-methylisoxazole-5-carboxylate (2.0 g,11.7 mmol) and K₂CO₃ (4.0 g, 29 mmol) in ethanol (50 mL) was heated at40° C. for a total of 26 h. Methyl iodide (0.8 mL, 13 mmol) was addedafter 1 h and an additional 3 times during the next 25 h. The solutionwas filtered and reduced in vacuo (according to ¹H NMR, a 1:1 mixture ofthe title compound and ethyl 3-methoxy-4-methylisoxazole-5-carboxylatewas obtained). Flash chromatography (silica gel, eluent:dichloromethane/diethyl ether=9:1 then 1:1) gave ethyl3-Methoxy-4-methylisoxazole-5-carboxylate as a yellow oil (0.40, 18%)and title compound (0.45 g, 21%). A small sample of the latter wasrecrystallized (EtOAc/heptane) to give colorless crystals: mp 64-65° C.Crude title compound was used in the next step without furtherpurification.

(RS)-2-Amino-3-(5-carboxy-2,3-dihydro-2-methyl-3-oxoisoxazol-4-yl)propionicAcid Hydrate (Comp 5)

The title compound was obtained by processes analogeous to those ofsteps 2)-6) of Example 1 using the product of 1) above (70 mg,colourless crystals, 72%). Mp 211-212° C. (dec); ¹H NMR (DMSO-d₆) δ2.87(dd, 1 H), 2.97 (dd, 1 H), 3.43 (s, 3 H), 3.92 (dd, 1 H); ¹³C NMR(DMSO-d₆) δ23.10, 32.32, 51.79, 106.51, 158.59, 162.37, 166.64, 170.35;MS ((M+H)⁺) m/z 231. Anal. (C₈H₁₀N₂O₆.0.25H₂O) calcd, C, 40.94; H, 4.51;N, 11.94; found, C, 40.93; H, 4.55; N, 11.71.

The following compound was prepared in a similar way:

(RS)-2-Amino-3-(5-carboxy-2-ethyl-2,3-dihydro-3-oxo-isoxazol-4-yl)propionicAcid Monohydrate (Comp. 6)

¹H NMR (D₂O, 1,4-dioxane d 3.70) δ1.28 (t, 3 H), 3.19 (d, 2 H), 4.01 (q,2 H), 4.18 (t, 1 H); ¹³C NMR (D₂O, 1,4-dioxane δ67.40) δ12.87, 23.85,42.31, 53.27, 110.57, 159.88, 162.65, 166.67, 172.55; MS ((M+H)⁺) m/z245. Anal. (C₉H₁₂N₂O₆.H₂O) calcd, C, 41.22; H, 5.38; N 10.68; found, C,41.28; H, 4.74; N, 10.27.

Example 3 (S)-2-Amino-3-(5-carboxy-3-ethoxyisoxazol-4-yl)propionic Acid(Comp (S)-2) (R)-2-Amino-3-(5-carboxy-3-ethoxyisoxazol-4-yl)propionicAcid (Comp (R)-2) 1)5-(4,5-Dihydro-4,4-dimethyl-1,3-oxazol-2-yl)-3-ethoxy-4-methylisoxazole

3-Ethoxy-4-methylisoxazole-5-carbonitrile (2.6 g, 17.1 mmol), 5.4 MNaOMe in MeOH (0.6 mL, 3.4 mmol) and EtOH (80 mL) was stirred at roomtemperature for 30 min. Acetic acid (2.2 mL, 39.3 mmol) and2-amino-2-methylpropan-1-ol (1.8 mL, 18.8 mmol) were added, and theresulting mixture was boiled under reflux for 20 h. The reaction mixturewas cooled, added water (100 mL) and extracted with EtOAc (3×100 mL).The organic extracts were washed with 1 M NaOH (50 mL), brine, dried(MgSO₄) and evaporated in vacuo. The residue was dissolved in EtOH (60mL), a solution of KOH (1.8 g, 32 mmol) in water (12 mL) was added, andthe mixture was stirred at room temperature for 20 h. EtOH was removedin vacuo, water was added (80 mL) and the aqueous phase extracted withEtOAc (3×100 mL). The organic extracts were washed with brine, dried(MgSO₄) and evaporated in vacuo. Flash chromatography (silica gel,eluent: EtOAc/heptane/triethylamine=75:25:1) gave crude title compoundas a yellow oil (2.0 g, 52%).

2)4-(Bromomethyl)-5-(4,5-dihydro-4,4-dimethyl-1,3-oxazol-2-yl)-3-ethoxyisoxazole

5-(4,5-Dihydro-4,4-dimethyl-1,3-oxazol-2-yl)-3-ethoxy-4-methylisoxazole(2.0 g, 8.9 mmol), NBS (1.75 g, 9.8 mmol) and tetrachloromethane (150mL) was boiled under reflux for 5 h. The mixture was cooled, filteredand concentrated in vacuo. Flash chromatography (silica gel, eluent:toluene/EtOAc/triethylamine=100:10:1) gave the title compound as ayellow oil (2.0 g, 74%).

3)(2S,5R)-2,5-Dihydro-2-{[5-(4,5-dihydro-4,4-dimethyl-1,3-oxazol-2-yl)-3-ethoxyisoxazol-4-yl]methyl}-5-isopropyl-3,6-dimethoxypyrazineand(2R,2R)-2,5-Dihydro-2-{[5-(4,5-dihydro-4,4-dimethyl-1,3-oxazol-2-yl)-3-ethoxyisoxazol-4-yl]methyl}-5-isopropyl-3,6-dimethoxypyrazine

A 1.6 M solution of butyllithium in hexane (1.9 mL, 3.0 mmol) was addedto a precooled (−78° C.) solution of(2R)-(−)-2,5-dihydro-2-isopropyl-3,6-dimethoxypyrazine (0.5 mL, 2.8mmol) in anhydrous tetrahydrofuran (8 mL). Stirring was continued at−78° C. for 10 min,4-(bromomethyl)-5-(4,5-dihydro-4,4-dimethyl-1,3-oxazol-2-yl)-3-ethoxyisoxazole(0.85 g, 2.8 mmol) dissolved in tetrahydrofuiran (5 mL) was added andthe resulting mixture stirred at −78° C. for 4.5 h. The reaction mixturewas allowed to warm to room temperature and concentrated in vacuo. Theresidue was dissolved in diethyl ether (40 mL) and poured onto anice/water mixture (40 mL). The layers were separated and the aqueousphase extracted with diethyl ether (2×40 mL). The organic extracts werewashed with brine, dried (MgSO₄) and concentrated in vacuo. Flashchromatography (silica gel, eluent: heptane/EtOAc=3:1) gave the(2S,5R)-title compound as a yellow oil (0.65 g, 57%): de=99.2%(retention time ca. 38 min). Further elution afforded crude(2R,5R)-title compound as a yellow oil (38 mg, 3%).

4)(2R,5S)-2,5-Dihydro-2-{[5-(4,5-dihydro-4,4-dimethyl-1,3-oxazol-2-yl)-3ethoxyisoxazol-4-yl]methyl}-5-isopropyl-3,6-dimethoxypyrazineand(2S,5S)-2,5-Dihydro-2-{[5-(4,5-dihydro-4,4-dimethyl-1,3-oxazol-2-yl)-3-ethoxyisoxazol-4-yl]methyl}-5-isopropyl-3,6-dimethoxypyrazine

The title compounds were obtained by a procedure as described in step 3)above using (2S)-(+)-2,5-dihydro-2-isopropyl-3,6-dimethoxypyrazine asstarting material. Flash chromatography (silica gel, eluent:heptane/EtOAc=3:1) to give (2R,5S)-title compound as a yellow oil (0.8g, 54%): de >99.2% (retention time ca. 38 min). Further elution affordedcrude (2S,5S)-title compound as a yellow oil (60 mg, 4%).

5) (S)-2-Amino-3-(5-carboxy-3-ethoxyisoxazol-4-yl)propionic Acid (Comp(S)-2)

A suspension of(2S,5R)-2,5-dihydro-2-{[5-(4,5-dihydro-4,4-dimethyl-1,3-oxazol-2-yl)3-ethoxyisoxazol-4-yl]methyl}-5-isopropyl-3,6-dimethoxypyrazine(0.6 g, 1.5 mmol) in 1 M trifluoroacetic acid (200 mL) was boiled underreflux for 5 h. The reaction mixture was concentrated in vacuo (2 mL),the residue dissolved in water (50 mL) and washed with EtOAc (3×50 mL).The aqueous phase was filtered, evaporated in vacuo to dryness and theresidue treated with water (10 mL). The precipitate which formed wasstirred at room temperature for 24 h, collected by filtration andrecrystallized (water) to afford compound (S)-2 as colourless crystals(0.12 g, 33%): mp 259-261° C. (dec); ee >99% (retention time ca. 30min); ¹H NMR (DMSO-d₆) δ1.34 (t, 3 H), 2.90 (dd, 1 H), 3.03 (dd, H),3.96 (dd, 1 H), 4.23 (q, 2 H); MS ((M+H)⁺) m/z 245. Anal. (C₉H₁₂N₂O₆)calcd, C, 44.27; H, 4.95; N, 11.47; found, C, 44.45; H, 4.96; N, 11.46.

6) (R)-2-Amino-3-(5-carboxy-3-ethoxyisoxazol-4-yl)propionic Acid (Comp.(R)-2)

A stirred solution of(2R,5S)-2,5-dihydro-2-{[5-(4,5-dihydro-4,4-dimethyl-1,3-oxazol-2-yl)-3-ethoxyisoxazol-4-yl]methyl}-5-isopropyl-3,6-dimethoxypyrazine(0.6 g, 1.5 mmol) and MeOH (7 mL) was added 0.25 M HCl (74 mL, 7.4mmol), and the resulting mixture stirred at room temperature for 2 h. pHwas adjusted to about 7 by addition of aqueous ammonia (0.5 M) and theMeOH removed in vacuo. pH was adjusted to 8-9 by addition of aqueousammonia (0.5 M) and the aqueous phase extracted with EtOAc (4×50 mL).The organic extracts were washed with brine, dried (MgSO₄) andconcentrated in vacuo. The residue was suspended in 1 M HCl and themixture boiled under reflux for 4.5 h. The reaction mixture wasconcentrated in vacuo (2 mL), the residue dissolved in water (50 mL) andwashed with EtOAc (3×50 mL). The aqueous phase was filtered, evaporatedin vacuo to dryness and the residue treated with water (10 mL). Theprecipitate which formed was stirred at room temperature for 2 h,collected by filtration and recrystallized (water) to afford compound(R)-2 as colorless crystals (0.13 g, 36%): mp 258-260° C. (dec); ee >99%(retention time ca. 50 min); ¹H NMR (DMSO-d₆) δ1.34 (t, 3 H), 2.90 (dd,1 H), 3.03 (dd, 1 H), 3.96 (dd. 1 H), 4.23 (q, 2 H); MS ((M+H)⁺) m/z245. Anal. (C₉H₁₂N₂O₆) calcd, C, 44.27; H, 4.95; N, 11.47; found, C,44.56; H, 4.95; N, 11.53.

Example 4(RS)-2-Amino-3-[3-ethoxy-5-(1H-1,2,4-triazol-3-yl)isoxazol-4-yl]propionicAcid Hydrate (Comp 7)N-[(Dimethylamino)methylidene]-3-ethoxy-4-methylisoxazole-5-carboxamide

A solution of 3-ethoxy-4-methylisoxazole-5-carboxamide (3.5 g, 21 mmol)in N,N-dimethylformamide dimethyl acetal (15 mL) was stirred at 120° C.for 15 min. After being cooled, the title compound was collected as acolourless crystals (4.2 g, 91%).

3-(3-Ethoxy-4-methylisoxazol-5-yl)-1H-1,2,4-triazole

To a solution of hydrazine hydrate (0.6 mL, 12.4 mmol) in acetic acid(15 mL) was added N-(dimethylamino)methylidene3-ethoxy-4-methylisoxazole-5-carboxamide (1.8 g, 8.0 mmol). The reactionmixture was stirred at 90° C. for 15 min and then left at roomtemperature to crystallize affording pure title compound (1.2 g, 77%):mp 194-196° C. Water was added (40 mL) and the aqueous phase wasextracted with EtOAc (3×30 mL). The organic extracts were washed withbrine, dried (MgSO₄) and concentrated in vacuo to give crude titlecompound (0.3 g, 20%). The two crops were combined.

3-(3-Ethoxy-4-methylisoxazol-5-yl)-1-trityl-1H-1,2,4-triazole

3-(3-Ethoxy-4-methylisoxazol-5-yl)-1H-1,2,4-triazole (1.1 g, 5.7 mmol),triethylamine (2.5 mL, 18 mmol) and DMF (20 mL) was added tritylchloride (1.6 g, 5.7 mmol) in DMF (5 mL). The mixture was stirred atroom temperature for 5 h and poured onto an ice/water mixture (200 mL).The aqueous phase was extracted with diethyl ether (3×200 mL) and theorganic extracts were washed with an aqueous solution of Na₂CO₃ (10%)(200 mL) and brine (200 mL). The solution was dried (Na₂SO₄) andconcentrated in vacuo to give crude title compound (2.5 g). A smallsample was crystallized (EtOAc) to give a single isomer as colourlesscrystals: mp 181-183° C. The crude product was used in the next stepwithout further purification.

3-[4-(Bromomethyl)-3-ethoxyisoxazol-5-yl]-1-trityl-1H-1,2,4-triazole

A mixture of3-(3-ethoxy-4-methylisoxazol-5-yl)-1-trityl-1H-1,2,4-triazole (2.4 g,5.5 mmol) and NBS (1.1 g, 6.2 mmol) in tetrachloromethane (150 mL) wasboiled under reflux for 3 h. The reaction mixture was cooled, filteredand concentrated in vacuo to give crude title compound (2.8 g). Thecrude product was used in the next step without further purification.

Ethyl2-Acetamido-3-[3-ethoxy-5-(1-trityl-1H-1,2,4-triazol-3-yl)isoxazol-4-yl]-2-(ethoxycarbonyl)propionate

A mixture of diethyl acetamidomalonate (1.3 g, 6.0 mmol) and potassiumtert-butoxide (0.73 g, 6.5 mmol) in N-methylpyrrolidone (30 mL) wasstirred at room temperature for 30 min.3-[4-(Bromomethyl)-3-ethoxyisoxazol-5-yl]-1-trityl-1H-1,2,4-triazole(2.8 g, 5.4 mmol) in N-methylpyrrolidone (20 mL) was added (temp 22-28°C.) and the resulting mixture was stirred at room temperature for 2 h.The reaction mixture was poured onto an ice/water mixture (250 mL) andthe aqueous phase was extracted with EtOAc (3×250 mL). The organicextracts were washed with an aqueous solution of potassium tert-butoxideand brine, dried (Na₂SO₄) and concentrated in vacuo. Flashchromatography (silica gel, eluent: EtOAc/heptane/triethylamine=50:50:2)gave the title compound (2.2 g, 62%): mp 145-149° C.

(RS)-2-Amino-3-[3-ethoxy-5-(1H-1,2,4-triazol-3-yl)isoxazol-4-yl]propionicAcid Hydrate (Comp 7)

A suspension of ethyl2-acetamido-3-[3-ethoxy-5-(1-trityl-1H-1,2,4-triazol-3-yl)isoxazol-4-yl]-2-(ethoxycarbonyl)propionate(1.5 g, 2.3 mmol) in 1 M HCl (150 mL) was boiled under reflux for 24 h.The solution was cooled, washed with diethyl ether (2×150 mL) anddichloromethane (150 mL), filtered and concentrated in vacuo. Water wasadded (5 mL) and the pH adjusted to about 3.5 by addition of NaOH (0.1 Mand 1 M) affording Compound 7 by filtration (0.35 g, 56%): mp 225-227°C. (dec); ¹H NMR (DMSO-d₆) δ1.38 (t, 3 H), 2.94 (dd, 1 H), 3.18 (dd, 1H), 3.58 (dd, 1 H), 4.30 (q, 2 H), 8.64 (s, 1 H); ¹³C NMR (DMSO-d₆)δ14.52, 23.60, 53.30, 65.93, 104.25, 146.18, 150.87, 158.44, 169.47,170.51; MS ((M+H)⁺) m/z 268. Anal. (C₁₀H₁₃N₅O₄.0.25H₂O) calcd, C, 44.20;H, 5.01; N, 25.77; found, C, 44.42; H, 5.29; N, 25.52.

Example 5(RS)-2-Amino-3-[3-ethoxy-5-(5-tetrazolyl)isoxazol-4-yl]propionic acid(Comp. 8)

Was prepared by a method analogeous to the method of Example 4 fromethyl2-acetamido-3-[3-ethoxy-5-(tetrazol-5-yl)isoxazol-4-yl]-2-(ethoxycarbonyl)propionate.

Example 6 (RS)-2-Amino-3-(3-benzyloxy-5-carboxyisoxazol-4-yl)propionicAcid (Comp. 9)

(RS)-2-Amino-3-(5-carboxy-3-hydroxyisoxazol-4-yl)propionic acid (3.5 g,11.8 mmol) and a solution of HCl in ethanol (50 mL) was boiled underreflux for 2.5 h and evaporated to dryness in vacuo to give ethyl(RS)-2-amino-3-(5-ethoxycarbonyl-3-hydroxyisoxazol-4-yl)propionate (4.15g, 100%).

A mixture of di-tert-butyl dicarbonate (3.1 g, 14 mmol), triethylamine(3.8 g, 37 mmol) and 1,4-dioxane (15 mL) was added to a solution ofethyl (RS)-2-amino-3-(5-ethoxycarbonyl-3-hydroxyisoxazol-4-yl)propionate(4.15 g, 11.7 mmol) in a water/1,4-dioxane (1:1) (50 mL), and theresulting mixture was stirred at room temperature for 16 h. The1,4-dioxane was evaporated in vacuo, and the aqueous phase was acidifiedwith dilute aqueous HCl. The aqueous phase was extracted with ethylacetate, and the organic extracts washed with water, brine, dried(MgSO₄) and concentrated in vacuo. Flash chromatography (SiO₂, eluent:heptane/ethyl acetate/acetic acid (1:1, 4%)) gave ethyl(RS)-2-tert-butoxycarbonylamino-3-(5-ethoxycarbonyl-3-hydroxyisoxazol-4-yl)propionateas an oil (4.1 g, 92%).

A mixture of ethyl(RS)-2-tert-butoxycarbonylamino-3-(5-ethoxycarbonyl-3-hydroxyisoxazol-4-yl)propionate(3.2 g, 8.6 mmol), K₂CO₃ (2.4 g, 17.2 mmol) in acetone (40 mL) washeated to reflux temperature. Benzyl bromide (2.2 g, 12.9 mmol) wasadded, and the mixture was boiled under reflux for 1.5 h. Concentratedin vacuo and subjected to flash chromatography (SiO₂, eluent:heptane/ethyl acetate (2:1)) to give ethyl(RS)-2-[(tert-butoxycarbonyl)amino]-3-[3-benzyloxy-5-(ethoxycarbonyl)isoxazol-4-yl]propionate(1.64 g, 41%) and ethyl(RS)-2-[(tert-butoxycarbonyl)amino]-3-(2-benzyl-5-ethoxycarbonyl-2,3-dihydro-3-oxoisoxazol-4-yl)propionate(0.7 g, 18%).

A mixture of ethyl(RS)-2-[(tert-butoxycarbonyl)amino]-3-[3-benzyloxy-5-(ethoxycarbonyl)isoxazol-4-yl]propionate(0.65 mg, 1.4 mmol) and 1 M NaOH (50 mL) was boiled under reflux for 16h. The mixture was cooled (5° C.), acidified with dilute aqueous HCl,and concentrated in vacuo. The residue was recrystallized from water togive (RS)-2-amino-3-(3-benzyloxy-5-carboxyisoxazol-4-yl)propionic acid(0.1 g, 23%): mp 209-211° C. (dec); ¹H NMR (DMSO-d₆) δ2.95 (dd, 1 H),3.05 (dd, 1 H), 3.99 (t, 1 H), 5.26 (s, 2 H), 7.31-7.52 (m, 5 H); MS((M+H)⁺) m/z 307. Anal. calcd, C, 54.89; H, 4.62; N, 9.15; found, C,54.31; H, 4.56; N, 8.97.

The following compounds were prepared in a similar manner:

(RS)-2-Amino-3-(3-propoxy-5-carboxyisoxazol-4-yl)propionic Acid (Comp.10)

Mp. 250-251° C. (dec). ¹H NMR (D₂O, dioxane,1 M NaOD) d 0.95 (t, 3 H),1.76 (se, 2 H), 2.78 (dd, 1 H), 2.90 (dd, 1 H), 3.42 (dd, 1 H), 4.17 (t,2 H). ¹³C NMR d 12.3, 24.4, 29.8, 58.3, 74.9, 111.5, 164.3, 166.6,173.9, 184.8. MS ((M+H)⁺) m/z 259. Anal. calcd, C, 46.51; H, 5.46; N,10.85; found C, 46.43; H, 5.41; N, 10.54.

(RS)-2-Amino-3-(3-butoxy-5-carboxisoxazol-4-yl)propionic Acid (Comp. 11)

Mp 238-240° C. (dec). ¹H NMR (D₂O, dioxane, 1 M NaOD) d 0.95 (t, 3 H),1.43 (se, 2 H), 1.76 (qui, 2 H), 2.8 (dd, 1 H), 2.91 (dd, 1 H), 3.44(dd, 1 H), 4.25 (t, 2 H). ¹³C NMR NMR (D₂O, dioxan, 1 M NaOD) d 13.79,19.30, 27.90, 31.03, 56.39, 71.27, 109.65, 162.39, 164.72, 172.02,182.92. MS ((M+H)⁺) m/z 273. Anal. calcd. C, 48.53; H, 5.92; N, 10.29;found, C, 48.80; H, 5.99; N, 10.34.

(RS)-2-Amino-3-(3-allyloxy-5-carboxyisoxazol-4-yl)propionic Acid (Comp.12)

Mp 239-240° C. (dec). ¹H NMR (DMSO-d₆) d 2.93 (dd, 1 H), 3.06 (dd, 1 H),3.99 (dd, 1 H), 4.73 (d, 2 H), 5.29 (dd, 1 H), 5.44 (dd, 1 H), 6.05 (dq,1 H).

Furtermore the following compounds are prepared similarly:

(RS)-2Amino-3-[3-(trans-2-but-ene-oxy)-5carboxyisoxazol-4-yl]propionicAcid

(RS)-2Amino-3-[3-(methyl-2-but-ene-oxy)-5carboxyisoxazol-4-yl]propionicAcid

Example 7(RS)-2-Amino-3-(2-benzyl-5-carboxy-2,3-dihydro-3oxisoxazol-4-yl)propionicAcid, Hydrochloride, Monohydrate (Comp. 13)

A mixture of ethyl(RS)-2-[(tert-butoxycarbonyl)amino]-3-(2-benzyl-5-ethoxycarbonyl-2,3-dihydro-3-oxoisoxazol-4-yl)propionate(0.9 g, 1.9 mmol) and 1 M HCl was boiled under reflux for 5 h. Themixture was evaporated in vacuo to dryness (0.56 g, 80%): mp 146-148° C.(dec); ¹H NMR (DMSO-d₆) δ3.08 (dd, 1 H), 3.19 (dd, 1 H), 4.17 (br s, 1H), 5.16 (s, 2 H), 7.24-7.45 (m, 5 H); MS ((M+H)⁺) m/z 307. Anal. calcd,C, 46.60; H, 4.76; N, 7.77; found, C, 46.88; H, 4.81; N, 7.96.

Example 8 Benzyl(RS)-2-Amino-3-(5-benzyloxycarbonyl-3-ethoxyisoxazol-4-yl)propionateHydrochloride (Comp. 14)

A mixture of di-tert-butyl dicarbonate (1.1 g, 4.9 mmol), NaHCO₃ (1.1 g,13 mmol) and 1,4-dioxane (3 mL) was added to a solution of(RS)-2-amino-3-(5-carboxy-3-ethoxyisoxazol-4-yl)propionic acid (1.0 g,4.1 mmol) in a water/1,4-dioxane (1:1) (10 mL), and the resultingmixture was stirred at room temperature for 16 h. The 1,4-dioxane wasevaporated in vacuo, and the aqueous phase was acidified with diluteaqueous HCl. The aqueous phase was extracted with ethyl acetate, and theorganic extracts washed with water and brine. Dried (MgSO₄),concentrated in vacuo and subjected to flash chromatography (SiO₂,eluent:, ethyl acetate/ethanol/acetic acid (3:1, 4%)) to give(RS)-2-[(tert-butoxycarbonyl)amino]-3-(5-carboxy-3-ethoxyisoxazol-4-yl)propionicacid (1.4 g, 100%)

A mixture of(RS)-2-[(tert-butoxycarbonyl)amino]-3-(5-carboxy-3-ethoxyisoxazol-4yl)propionicacid (1.4 g, 4.1 mmol), benzyl bromide (1.4 g, 8.2 mmol) inbenzene/tetrahydrofuran (4:1) was added1,8-diazabicyclo[5.4.0]undec-7-ene (1.3 g, 8.6 mmol) and the resultingmixture was boiled under reflux for 3 h. The mixture was filtered andevaporated in vacuo. Flash chromatography (SiO₂, eluent:, ethylacetate/heptane (1:3)) gave benzyl(RS)-2-[(tert-butoxycarbonyl)amino]-3-(5-benzyloxycarbonyl-3-ethoxyisoxazol-4-yl)propionateas an oil (1.9 g, 86%).

A mixture of benzyl(RS)-2-[(tert-butoxycarbonyl)amino]-3-(5-benzyloxycarbonyl-3-ethoxyisoxazol-4-yl)propionate(1.9 g, 3.6 mmol) and a saturated solution of HCl in dietyl ether (40mL) was boiled under reflux for 2 h. The formed crystals were collectedby filtration, stirred with ethyl acetate, and collected by filtration(0.53 g, 32%): mp 142-144° C.; ¹H NMR (DMSO-d₆) δ1.32 (t, 3 H), 3.17(dd, 1 H), 3.25 (dd, 1 H), 4.17-4.32 (m, 3 H), 5.09 (dd, 2 H), 5.39 (s,2 H), 7.24-7.53 (m, 10 H); MS ((M+H)⁺) m/z 425. Anal. calcd, C, 59.93;H, 5.48; N, 6.08; found, C, 59.70; H, 5.49; N, 6.26.

Example 9 Ethyl(RS)-2-Amino-3-(3-ethoxy-5-ethoxycarbonylisoxazol-4-yl)propionate,Oxalate (Comp. 15)

A mixture of (RS)-2-amino-3-(5-carboxy-3-ethoxyisoxazol-4-yl)propionicacid (2.0 g, 8.2 mmol) and a solution of HCl in ethanol (35 mL) wasboiled under reflux for 3 h to give ethyl(RS)-2-amino-3-(5-carboxy-3-ethoxyisoxazol-4-yl)propionate. Ethyl(RS)-2-Amino-3-(5-carboxy-3-ethoxyisoxazol-4-yl)propionate (0.6 g) wasadded a dilute solution of NaOH, and the aqueous phase was extractedwith ethyl acetate. The organic extracts were washed with brine, dried(MgSO₄), filtered and evaporated to dryness in vacuo. The residue wasdissolved in acetone (6 mL) and added a solution of oxalic acid (0.14 g,1.6 mmol) in acetone (6 mL), and the formed precipitate was collected byfiltration (110 mg, 10%): mp 159-161° C.; ¹H NMR (DMSO-d₆) δ1.11 (t, 3H), 1.32 (t, 3 H), 1.36 (t, 3 H), 3.02 (dd, 1 H), 3.11 (dd, 1 H),3.98-4.16 (m, 3 H) 4.32 (q, 2 H), 4.37 (q, 2 H); MS ((M+H)⁺) m/z 301.Anal. calcd, C, 46.15; H, 5.69; N, 7.18; found, C, 46.38; H, 5.69; N,7.36.

Example 10 Butyl(RS)-2-amino-3-(5-butoxycarbonyl-3-ethoxyisoxazol-4-yl)propionate,oxalate (Comp. 16)

The compound was obtained in a similar manner as described in Example 9by using a solution of HCl in butanol. mp 120-121° C.; ¹H NMR (DMSO-d₆)δ0.84 (t, 3 H), 0.92 (t, 3 H), 1.14-1.31 (m, 2 H), 1.31-1.51 (m, 4 H),1.37 (t, 3 H) 1.62-1.75 (m, 2 H), 3.01 (dd, 1 H), 3.13 (dd, 1 H),3.98-4.09 (m, 3 H), 4.16-4-436 (m, 4 H); MS ((M+H)⁺) m/z 357. Anal.calcd, C, 51.11; H, 6.79; N, 6.28; found, C, 51.06; H, 6.82; N, 6.35.

Example 11[4-(2-Amino-3,4-dioxocyclobut-1-en-1-yl)aminomethyl]-3-ethoxyisoxazole-5-carboxylicAcid (Comp. 17) Ethyl 3-Ethoxy-4-methylisoxazole-5-carboxylate

Acetyl chloride (25 mL, 0.35 mol) was added to EtOH (250 mL) at 0° C.and the solution was stirred at 0° C. for 20 min. A solution of3-ethoxy-4-methylisoxazole-5-carboxylic acid (WO95/12587,A1) (18 g, 0.10mol) in EtOH (20 ml) was added and the resulting mixture was boiledunder reflux for 4 h. The mixture was cooled, added NaHCO₃ (200 mL) andextracted with diethylether (3×300 mL). The organic extracts were dried(MgSO₄) and concentrated in vacuo to afford crude title compound (18 g,86%).

Ethyl 4-Bromomethyl-3-ethoxyisoxazole-5-carboxylate

Ethyl 3-Ethoxy-4-methylisoxazole-5-carboxylate (18 g, 91 mmol), NBS(17.5 g, 100 mmol), dibenzoyl peroxide (1 g, 4.1 mmol) intetrachloromethane (500 mL) was boiled under reflux for 16 h. Themixture was cooled, filtered and concentrated in vacuo to afford thecrude title compound (24.5 g, 97%).

Ethyl 3-Ethoxy-4-phthalimidomethylisoxazole-5-carboxylate

A solusion of ethyl 4-bromomethyl-3-ethoxyisoxazole-5-carboxylate (5 g,17.9 mmol) in DMF (85 mL) was added to a suspension of potassiumphthalimid (3.6 g, 19,7 mmol) in DMF (125 mL) at 90° C. The resultingmixture was stirred at 90° C. for 40 min, then cooled and concentratedin vacuo. Water (250 mL) was added and the aqueous phase was extractedwith diethylether (2×200 mL). The organic extracts were dried (MgSO₄)and concentrated in vacuo to give a crude product which wasrecrystallized (EtOH) to yield the title compound (3.70 g, 60%): mp93-94° C.

4-Aminomethyl-3-ethoxyisoxazole-5-carboxylic Acid Hydrochloride

A solution of ethyl 3-ethoxy-4-phthalimidomethylisoxazole-5-carboxylatein 1 M NaOH was boiled under reflux for 45 min. The mixture was cooled,added concd HCl and extracted with diethylether (3×400 ml). The organicextracts were concentrated in vacuo, added 1 M HCl (600 mL) and boiledunder reflux for 1 h. After cooling the mixture was washed withdiethylether (3×600 mL) and concentrated in vacuo to give a crudeproduct which was recrystallized (acetic acid) to yield the titlecompound (1.5 g, 82%): mp 215-216° C. (dec).

[4-(2-Amino-3,4-dioxocyclobut-1-en-1-yl)aminomethyl]-3-ethoxyisoxazole-5-carboxylicAcid

To a solution of 4-aminomethyl-3-ethoxyisoxazole-5-carboxylic acidhydrochloride (1.2 g, 5.4 mmol) and3-amino-4-ethoxy-cyclobut-3-en-1,2-dione (0.60 g, 5.9 mmol) in EtOH (300ML) was added 1 M NaOH (12 mL). The resulting suspension was stirred atroom temperature for 16 h, then concentrated in vacuo, added water (100mL) and washed with EtOAc (2×100 mL). The pH was adjusted to ca. 3 byaddition of 1 M HCl. The precipitate was filtered off and recrystallized(water) to afford the title compound as a yellow powder (0.71 g, 47%):mp 236-238° C. (dec). ¹H NMR (DMSO-d₆) d 1.30 (t, 3 H), 4.22 (q, 2 H),4.68 (bs, 2 H). ¹³C NMR (DMSO-d₆) δ14.41, 35.27, 65.54, 107.16, 159.14,163.54, 168.71, 169.15, 169.73, 183.20, 183.34. MS ((M+H)⁺) m/z 282.Anal. (C₁₁H₁₁N₃O₆, 2.25 H₂O) calcd, C, 41.06; H, 4.86; N, 13.06; found,C, 41.16; H, 4.46; N, 12.96.

Pharmacology

The compounds of the invention were tested in accordance with thefollowing well recognised and reliable test methods.

[³H]AMPA Binding

In this test the affinity of a drug for AMPA receptors is determined bymeasuring the ability to displace [³H]AMPA from AMPA receptors.

The test was carried out in accordance with a modified version of themethod of Honoré, T. and Nielsen, M., Neurosci.Lett. 1985, 54, 27-32.The test was carried out in the presence of KSCN. This means that onlythe [³H]AMPA high affinity binding sites were labelled.

The membrane preparations used were obtained in accordance with themethod of Ransom, R. W. and Stec, J. Neurochem. 1988, 51, 830-836.

The Cortical Wedge Model

The Cortical wedge model is a test in which slices of rat brain isexamined in vitro in order to quantify the effect of ligands at thevarious Glu-receptors and evaluate the pharmacological profile of theligands (i.e. agonist/antagonist properties). The test was performed asdescribed by Harrison, N. L. and Simmonds, M. A. Br.J.Pharmacol. 1985,84, 381-391 as modified according to Wheatley, P. L. Br.J.Pharmacol.1986, 87, 159P.

TABLE 1 Cortical Wedge Compound Profile EC₅₀ (μM) pK_(i) Receptorsubtype  1 Agonist 1.2 AMPA  2 Agonist 4.8 AMPA (S)-2 Agonist 4.4 AMPA(R)-2 Antagonist 3.28 AMPA  3 Agonist 40.0 AMPA  8 Agonist 2000 AMPA 10Agonist 80 AMPA 11 Part. Agonist 325 AMPA 12 Agonist 40 AMPA 13Antagonist 3.5 NMDA 17 Antagonist 3.3 NMDA

Result

The compounds were found to be excitatory amino acid (EAA) receptorligands. Some of the compounds were found to be agonists at the AMPAreceptors and other compounds were found to be selective AMPA or NMDAreceptor antagonists. The compounds showed activity in the μM range.

Formulation Examples

The pharmaceutical formulations of the invention may be prepared byconventional methods in the art.

For example: Tablets may be prepared by mixing the active ingredientwith ordinary adjuvants and/or diluents and subsequently compressing themixture in a conventional tabletting machine. Examples of adjuvants ordiluents comprise: corn starch, lactose, talcum, magnesium stearate,gelatine, lactose, gums, and the like. Any other adjuvant or additivecolourings, aroma, preservatives etc. may be used provided that they arecompatible with the active ingredients.

Solutions for injections may be prepared by solving the activeingredient and possible additives in a part of the vehicle, preferablysterile water, adjusting the solution to the desired volume,sterilisation of the solution and filling in suitable ampules or vials.Any suitable additive conventionally used in the art may be added, suchas tonicity agents, preservatives, antioxidants, etc.

What is claimed is:
 1. A (3-alkoxyisoxazol-4-yl)-substituted 2-aminocarboxylic acid derivative having general Formula I or II

wherein R₁ is hydrogen, C₁₋₆ alkyl, C₂₋₆ alkenyl, C₂₋₆ alkynyl,cycloalk(en)yl, cycloalk(en)yl-C₁₋₆alk(en/yn)yl orphenyl-C₁₋₆alk(en/yn)yl, the phenyl group being optionally substitutedwith CF₃, halogen, C₁₋₆ alkyl or C₁₋₆ alkoxy; A is a bond or a spacergroup selected from C₁₋₆ alkylene, C₂₋₆ alkenylene, C₂₋₆ alkynylene, andcycloalkylene; B is a group —CR_(a) (NR_(b)R_(c))—COOR₅ whereinR_(a)-R_(c) are independently hydrogen or C₁₋₆ alkyl, and R₅ is definedas R₁ or pivaloyloxymethyl, or B is a group of Formula III

 wherein R₂, R₃ and R₄ are independently selected from the groupconsisting of a) hydrogen, C₁₋₆ alkyl, C₂₋₆ alkenyl, C₂₋₆ alkynyl,cycloalk(en)yl, cycloalk(en)yl-C₁₋₆ alk(en/yn)yl, phenyl-C₁₋₆ alkyl,thienyl-C₁₋₆-alkyl, and b) C₁₋₆ alkyl, C₂₋₆ alkenyl and C₂₋₆ alkynyl inwhich one or more carbon atoms are replaced by N, O, and/or S, or R₃ andR₄ are connected, thereby forming a C₂-C₆ alkylene, C₂-C₆ alkenylene orC₂-C₆ alkynylene group, or R₄ and R₂ are connected in order to form aC₁-C₃ alkylene, C₂-C₃ alkenylene or C₂-C₃ alkynylene group optionallymono- or di-substituted with hydroxy or methyl, or to form CH₂—O—CH₂; Eis COOR₆, where R₆ is defined as R₅; X is O; Y is O or S; or apharmaceutically acceptable salt thereof.
 2. A compound of claim 1 whichhas Formula I.
 3. A compound of claim 1 which has Formula II.
 4. Acompound of claim 1, wherein R₆ is not hydrogen.
 5. A compound of claim1, wherein E is COOH.
 6. A compound of claim 1, wherein B is a group ofthe formula CR_(a)(NR_(b)R_(c))—COOR₅.
 7. A compound of claim 6, whereinR_(b) and R_(c) are hydrogen and R_(a) is hydrogen or C₁₋₆ alkyl.
 8. Acompound of claim 1, wherein R₅ is hydrogen.
 9. A compound of claim 1,wherein R₅ is not hydrogen.
 10. A compound of claim 1, wherein B is agroup of the formula III.
 11. A compound of claim 10, wherein R₂, R₃ andR₄ are hydrogen or C₁₋₆ alkyl, or R₄ and R₂ are connected in order toform a C₁-C₃ alkylene group.
 12. A compound of claim 11, wherein each ofR₂, R₃ and R₄ are hydrogen.
 13. A compound of claim 1, wherein Y isoxygen.
 14. A compound of claim 1, wherein Y is sulfur.
 15. A compoundof claim 1, wherein R₁ is C₁₋₆ alkyl, C₂₋₆ alkenyl or C₂₋₆ alkynyl. 16.A compound of claim 1, wherein A is a bond or C₁-C₃ alkylene.
 17. Acompound of claim 2, wherein A is a bond or C₁-C₃ alkylene, B is—CH(NH₂)—COOH or a group of Formula III wherein each of R₃, R₄ and R₂are hydrogen, Y is oxygen, and R₁ is C₁₋₆ alkyl, C₂₋₆ alkenyl or C₂₋₆alkynyl.
 18. A compound of claim 1 wherein R₆ is selected from the groupconsisting of C₁₋₆ alkyl phenyl-C₁₋₆, alk(en/yn)yl andpivaloyloxymethyl.
 19. A compound of claim 15 wherein R₁ is selectedfrom the group consisting of methyl, ethyl, propyl or propargyl.
 20. Acompound of claim 16 wherein said C₁₋₃ alkylene is methylene.
 21. Acompound of claim 17 wherein R₁ is selected from the group consisting ofmethyl, ethyl, propyl or propargyl.
 22. A pharmaceutical compositioncomprising a compound of claim 1 together with a pharmaceuticallyacceptable carrier or diluent.
 23. A method of treating cerebralischaemia, Huntington's disease, epileptic disorders, Parkinson'sdisease, Alzheimer's disease, schizophrenia, pain, depression oranxiety, said method comprising administering a therapeuticallyeffective amount of a compound of claim 1 to a patient in need thereof.